In interchangeable floppy-disk, recording devices, often referred to as diskette drives, there has been very little electronics built into the drive. Typically, the disk motor has been a DC motor driven at constant speed, and the recording head has been indexed to different tracks on the disk by a stepping motor. The interface between the drive and drive adapter has contained few signal lines, for example disk motor on/off, steps for the stepping motor control, read data and write data.
In the past if the drive failed, the drive usually interrupted the using system by just shutting down. However, in some systems a drive might not shut down because of the type of failure. In this event, more severe results could occur such as loss of data caused by overwriting, erasure or failure to read. To date there has been no way for the using system to know the cause of the failure and thus no way to attempt recovery.
With the advent of microprocessors, electronics in the diskette drives can offer more function. It is now possible to use a microprocessor in the drive to perform such functions as spindle motor control to control the speed of the disk, stepper motor control for more precise indexing of the recording head and fault detection of functions in the drive including diagnostic routines.
With computing power available on the drive, the interface between the drive and its adapter or using system could be made more sophisticated to take advantage of this computing power. However, for sake of compatibility with prior designs it is desirable to leave the interface unchanged. Also, to keep the cost of the drive low it is desirable to minimize the number of signal lines and associated buffers and gates between the drive and its adapter. Accordingly, the problem becomes how to take advantage of the computing power on the diskette drive and thus additional control and error information that might be available from the drive without changing the interface between the drive and its adapter or between the adapter and its using system.